Lisp — a high-level computer programming language specified in 1958, — pioneered many computer science concepts that we now take for granted. Today, you can interact with this historical computing language using a serial monitor, via the uLisp implementation which runs on a microcontroller. With the Visible Lisp Computer by David Johnson-Davies, contents of the Lisp workspace are displayed on an OLED screen, so you can see the program execution and garbage collection as it happens.
The device uses a specialized version of uLisp designed to run on arm boards, and this project is implemented in both an Adafruit ItsyBitsy M0 and a bare ATSAMD21E on a prototyping board (with a few extra needed components as described in this separate post). The controller interacts with the setup’s 64×48 I2C OLED display via relatively simple wiring, which represents allocated Lisp objects as white pixels on the screen.
This interesting representation does cause Lisp programs to run more slowly, so the display can be turned off if you so prefer. During the process, unneeded objects are freed automatically via garbage collection, which gives you more program space — and on-screen as black pixels. The Visible Lisp , and Lisp itself, looks like an interesting way to experiment with basic programming concepts, with the simple resource monitor serving as a great learning tool.